1. Field of the Invention
The present invention is related to telephones and more particularly to telephones having a hands-free mode of operation.
2. Background
Typical state-of-the-art telephones often have a hands-free or speakerphone mode of operation, hereinafter generically xe2x80x9cspeakerphone.xe2x80x9d Such a telephone may be located at a convenient location and placed in hands-free mode. Thereafter, speakers, e.g., teleconference participants, may remain stationary or move about within range of the speakerphone as desired. The speakerphone microphone picks up all surrounding sound including background noise. This sound is transmitted to a listener at the other end of the call. Traditional speakerphones have a single microphone and are omnidirectional such that voice of the speaker and background noise are equally received and passed on to the listener.
Occasionally, background noise may be such that hands free operation is difficult to use if usable at all. Often the background noise originates from a single source that may be located at a fixed location within the room, e.g., from a noisy air conditioner or, from outside of the room such as from street work. To compensate for this background noise the microphone sensitivity may be lowered and the speakers may be requested to speak up. Sometimes this works, sometimes it does not. Also, the noise may be such that setting the microphone sensitivity at one level is an unacceptable solution, e.g., a pulsating type noise.
Thus there is a need for a speakerphone with capability of selectively removing background noise to provide improved audio quality, especially during hands free operation.
It is a purpose of the invention to improve a signal noise ratio for telephones operating in hands free mode of operation;
It is another purpose of the invention to improve the audio quality provided to a listener at a receiving ends of a hands free call;
The present invention is a telephone having a hands-free mode of operation. The telephone includes a pair of microphones spaced apart from each other. Each microphone receives sound in hands-free mode of operation and provides audio signals representative of received sounds. The audio signals from each microphone may be converted to digital audio signals. The digital audio signals are presented to a fixed delay path and a variable delay path. Audio signals from both paths are combined and filtered in an adjustable filter to remove noise based upon a prior determination of the noise source location and the voice spectrum derived from the digital audio signals.
Additional benefits and features of the invention will be apparent from the following detailed description taken together with the attached drawings.